Surge Protector- Over Voltage Protector

[gocirino]

You guys seen these things sold yet?
Surge Protector- Over Voltage Protector for welding on cars....

http://www.sjdiscounttools.com/dfxdf601.html

[DesertRider33]

Never seen one before. Looks like hocus pocus to me. If it just connects from the positive to negative terminals of the battery, I don't see where it would be protecting anything in the car's downstream electronics. Disconnecting the battery would likely accomplish more than the device in question.

[transit]

I’ve used surge protectors at work to protect computer equipment from lightening strikes, surges from the power grid switching and bring backup generators online. These units are configured and rated to handle utility power, 120, 240, 480 volts single and three phase Y and Delta circuits at 100,000 to 6,000,000 Amp-seconds. And yes they do work. You can have your local utility install a consumer model for home use to protect your PC, DTV, etc. Well worth the expense to protect that $$$ PC and DTV.

The unit you are asking about uses the same technology, however “Heavy Duty” means very little. What counts are the Amp-seconds power it will absorb and the let-through voltage that it will reduce the spike to? If the let-through voltage is high then the computer gets zapped. It looks like the unit is clamped across the battery terminals, meaning that it must not turn-on at normal voltages [12-15V] and turn-on at something more than 15+ volts, not knowing what the maximum safe voltage a OBS computer will tolerate, cant say how much protection you get. I’d go with removing the battery cables until I know more.

[Sandy]

Yeh, if it's ordinary old school varistor the clamping times are probably too slow to do any good for the most delicate type of electronics.

This thing would have to have approvals from about ten different agencies before I'd go clipping some unknown and unproven device directly across any battery of mine.

The auto makers themselves give procedures for jump starting and charging and they never mention adjunct devices.

[westom]

Originally Posted by gocirino

You guys seen these things sold yet?
Surge Protector- Over Voltage Protector for welding on cars....

What are you trying to protect from? They have you believing you need it. Then have a solution - all in one big myth.

If a surge is on both sides of the battery, then the battery is a short circuit to (eliminates) that surge current (basic electrical circuit theory). That type surge is harmful only when a battery is disconnected. Why do you assume that type surge even exists?

If the surge is a typically destructive type, then it is equal on both sides of a battery. For example, a ten thousand volt surge on both side of the battery is a zero volt surge to that battery. That surge continues elsewhere to cause damage while neither the battery nor protector even see (react to) it.

Moving on to other myths:
First, if a surge exists, then the protector must be located where that surge is generated or incoming. Ineffective protectors will not even discuss the source. Otherwise you might realize different types of surges exist and that the protector does not provide that protection.

Second, protectors (including MOVs) are more than fast enough. Unfortunately, many people only know about protectors from hearsay and myths. Let themselves become a victim.

Third, no spec numbers are provided. That protector is probably the same ineffective circuit sold to protect computers. In this case, $40 for some ten cent protector components. What says it is probably a profitable scam? Does the word 'victim' apply? View its spec numbers. They are selling to many who know only because surge 'protector' sounds like surge 'protection'. Or who don't know what a surge is; therefore it must be necessary.

Fourth, an effective protector diverts. Any protector that absorbs (or blocks) surges is promoting a classic scam. Applies both to that SJ Discount device. And to $150 myths promoted when buying a TV or computer. A protector too close to electronics can even contribute to transistor damage.

[transit]

If you care to read more deeply.

http://en.wikipedia.org/wiki/Varistor

http://www.mcgsurge.com/products/dc/dc_series.htm

[westom]

Originally Posted by transit

If you care to read more deeply.
http://en.wikipedia.org/wiki/Varistor

Please quote the part you think is in disupte.

1) What was posted in quite in agreement with the Wikipedia citation.

2) Citing a sales brochure without quoting the relveant parts suggests your knowledge comes only from hearsay and sales myths.

3) What in your post is relevant to or helps the OP?

[Sandy]

Second, protectors (including MOVs) are more than fast enough. Unfortunately, many people only know about protectors from hearsay and myths. Let themselves become a victim.

That's quite the statement. So they are all equal regardless of cost or makeup? There's no difference in a DC current spike and an AC high frequency voltage spike and any ole "fast enough" 90¢ MOV will get the job done?

But back to the point of the post. Before you can design any sort of electrical protection device for delicate electronics you should know all the variables you need to protect against as well as all the variables the source is capable of producing. I really doubt that clamping some $40.00 sugar pill across the battery and battery leads is going to protect a chip from the white ball of lightning that makes you go blind if you weld without a hood.

[transit]

Originally Posted by westom

Please quote the part you think is in disupte.

1) What was posted in quite in agreement with the Wikipedia citation.

2) Citing a sales brochure without quoting the relveant parts suggests your knowledge comes only from hearsay and sales myths.

3) What in your post is relevant to or helps the OP?

No argument, just proving your point, you get what you pay for. As for getting deeply into the technical mo-jo, rise and fall times, signal vs. multiple strikes, ringing, negative pulse on a positive voltage curve, etc. there is no need. Lightning-surge protection is half séance and half scientific, lots of snake oil around. Go with a reputable manufacture and you can’t go wrong, we use Eton TVSS devices.

[westom]

Originally Posted by Sandy

That's quite the statement. So they are all equal regardless of cost or makeup? There's no difference in a DC current spike and an AC high frequency voltage spike and any ole "fast enough" 90¢ MOV will get the job done?

Some of the most expensive protectors do not even claim to do protection. Retail cost has little relation with what provides protection. Only useful number is the one found in the manufacturer numeric specs - such as the number not provided by SJ Discount.

What do spec numbers say? Few really understand. But to keep silent the one percent who really know what that device does, a scam manufacturer will provide no numbers. Then a deceived majority will recommend it to one another using hearsay. Massive profits result.

Only relevant numbers are spec numbers. "You get what you pay for?" Only when the customers routinely demand spec numbers. Better protectors often cost less since protectors are more often sold on myths, hearsay, and scams rather than on the science.

A DC current spike does not exist - better called an oxymoron. A DC current spike was a classic joke in EE school. One need only remember math taught in high school to appreciate what a 'DC spike' really is. Fourier analysis. That DC spike is a sum of numerous sinusoids - AC electricity. A more abrupt spike means even higher frequencies. That DC spike is also what Marconi, et al used to create the first radio communications.

Typical protector components are fast enough. Response time says nothing about a protector’s effectiveness.

Irrelevant is what that SJ Discount device does. Again, from any first course, a battery is a short circuit to any surge current. Anything the protector would do is made completely irrelevant by the battery. So they sell some ten cent protector parts for $40.